1. Field of the Invention
The present invention relates to an attenuation-amount adjusting circuit and an attenuation-amount adjusting method for adjusting an attenuation amount of a reproduction signal corresponding to reflected light (return light) from an optical disk. The present invention also relates to an optical disk drive device and an address-information acquiring method for detecting physical address information on the optical disk.
2. Description of the Related Art
In general, in a recordable optical disk, in irradiating a laser beam on a groove to write data in the optical disk, it is necessary to accurately detect linear velocity in each radial position and a physical position in the groove. The linear velocity is used for, for example, rotation control for the optical disk and generation of a master clock for recording. The physical position in the groove is used for, for example, determination of an accurate recording position in bit units and acquisition of physical address information on the optical disk.
In general, the groove is formed by a spiral groove and spiral lands. The groove and the lands have a pattern that meanders at a fixed period with respect to a circumferential direction (a tracking direction) of the optical disk. A marker such as a wobble pattern having a period shorter than the period of the wobble pattern described above, a pre-pit of a hollow shape, or a land pre-pit of a split shape that traverses the groove is formed in the groove according to a type of a pre-format of a medium.
An optical disk drive device that copes with the optical disk having such a structure irradiates a laser beam on the groove of the rotating optical disk and detects, from reflected light from the optical disk, data recorded in the groove, information (linear velocity) corresponding to the wobble pattern of the long period, information corresponding to the marker (physical address information in the groove), and the like.
In writing data in the optical disk, the optical disk drive device alternately irradiates, on the basis of recorded data, a laser beam having extremely high power compared with that in the case of readout (a laser beam of a writing level) and a laser beam having low power equivalent to that in the case of readout (a laser beam of a readout level). Consequently, a pit having a relatively low reflectance is formed in the groove and data is written in the optical disk only when the laser beam of the writing level is irradiated.
In this case, a light intensity of the reflected light from the optical disk is larger as a light intensity of the irradiated light is larger and as a reflectance on an irradiation surface is larger. However, a difference between light intensities of the laser beams of the writing level and the readout level is overwhelmingly large compared with a difference between reflectances in the groove. Thus, a magnitude of a light intensity of a laser beam is predominant over a magnitude of a light intensity of the reflected light from the optical disk. Therefore, a light intensity of reflected light (reflected light of the laser beam of the writing level) in a period in which a pit is formed by irradiation of the laser beam of the writing level is extremely larger than a light intensity of reflected light (reflected light of the laser beam of the readout level) in a period in which a pit is not formed by irradiation of the laser beam of the readout level. Thus, it is likely that a reproduction signal corresponding to the reflected light of the laser beam of the writing level is saturated. In particular, in recent years, a light intensity of the laser beam of the writing level increases because of an increase in speed and an increase in capacity of an optical disk. Thus, it is extremely highly likely that a reproduction signal corresponding to the reflected light of the laser beam of the writing level is saturated.
Therefore, it is conceivable to, for example, expand an upper limit of a dynamic range of a pickup, an integrated circuit for processing an output signal of the pickup, and the like. However, to expand the upper limit of the dynamic range of the pickup, the integrated circuit, and the like, it is necessary to increase a voltage of a power supply that supplies power to the pickup, the integrated circuit, and the like. As a result, power consumption increases.
It is also conceivable to, for example, uniformly attenuate amplitude levels of reproduction signals corresponding to the reflected light of the laser beam of the writing level and the reflected light of the laser beam of the readout level. However, in that case, an amplitude level of a reproduction signal corresponding to, when the laser beam of the writing level is irradiated on the marker, light corresponding to the marker (reflected light of the marker at the time of writing) included in the reflected light is not equal to an amplitude level of a reproduction signal corresponding to, when the laser beam of the readout level is irradiated on the marker, light corresponding to the marker (reflected light of the marker at the time of readout) included in the reflected light. Therefore, compared with a predetermined slice level, it is difficult to binarize these reproduction signals. As a result, it is extremely difficult to detect the physical address information in the groove.
Thus, in the past, for example, as described in JP-A-2002-334446, attenuation processing by an attenuator is applied to only the reproduction signal corresponding to the reflected light of the laser beam of the writing level.